[Medullary sponge kidney (MSK)] =is a condition in which a portion of the kidney known as the medullary pyramid is found to have dilated tubules (tubules are small tubes through which urine drains) and numerous small cysts (cysts are fluid filled hollow spaces). The cysts are small, measuring from 1 to 8mm, but are numerous. The cysts give the kidney, when cut, the appearance of a sponge – from which the name of “medullary sponge kidney” was coined. # Mechanism: These cysts and dilated ducts lead to poor drainage, making it easier for stones to form. These abnormalities can be seen throughout both kidneys or may be localized in only one part of a kidney. The stones formed in MSK tend to be numerous and scattered throughout the kidney. # What are the symptoms of medullary sponge kidney? Flank pain in 52% Microscopic blood in the urine in 36% Visible blood in the urine in 16% Urinary tract infection in 7% Abdominal pain in 7% Testicular pain in 4% Imaging for other causes in 4% # Complication Individuals with MSK most commonly present with kidney stones, urinary tract infections, or blood in the urine. In individuals with MSK who form stones, other metabolic abnormalities that predispose someone to form stones are also commonly found, including hypercalciuria (high calcium levels in the urine) and renal tubular acidosis (a disorder with the kidney’s handling of acids). It therefore appears that just having MSK by itself is not enough to form stones (30% of MSK patients don’t form stones). However, combine the abnormalities found in MSK with someone who has a metabolic tendency to form stones and you will often see an astounding number of stones developing throughout the kidneys. X-rays for patients with MSK are often impressive for the sheer numbers of stones seen. Not all those stones will necessarily be in a position to drop into the ureter and cause traditional stone symptoms. In order to do so, the stones need to have access to the hollow collecting system portion of the kidney. Instead, many are often embedded in the solid tissue of the kidney (the parenchyma) where they are unlikely to result in a stone passage. In some patients however, the non-obstructing stones seen in MSK can be associated with significant and chronic pain, even if they are not passing. The pain in this situation can be constant in nature, unlike the episodic pain traditionally seen with kidney stones. It is not certain what causes this pain but authors have proposed that the small numerous stones seen in MSK may cause obstruction of the small tubules and collecting ducts in the kidney, leading to the pain. This pain can be debilitating and treatment is challenging. Narcotic medication, even with large quantities, is often not adequate. Some success with pain control for MSK patients with this type of pain has been reported using laser lithotripsy (see below). The most common stone types in MSK are calcium oxalate and calcium phosphate. Thankfully, MSK does not commonly lead to kidney failure. # Treatment: Treatment for MSK focuses on prevention and treatment of stones, management of pain, and prevention of infections. There is no treatment available to fix or remove the small cysts and dilated tubules associated with the condition. In stone formers, maintaining a high fluid intake and treatment with hydrochlorothiazide (to lower urinary calcium) and/or potassium citrate (to raise urinary citrate) are used. Metabolic evaluation with urinary and blood testing can be used to identify specific metabolic abnormalities that increase a person’s risk for stones. In addition, some authors advocate the use of hydrochlorothiazide in all patients with MSK, even when urinary calcium levels are normal. Treatment for stones that have already formed include the same approaches used for other stone patients, including ureteroscopy, shockwave lithotripsy, or less frequently, percutaneous nephrolithotripsy. Due to the large number of stones formed in MSK and the fact that many of those stones may not be within the collecting system, it is not usually necessary or possible to completely eradicate stones in a patient with MSK. In patients who have chronic pain associated with MSK, ureteroscopy with laser lithotripsy (called “ureteroscopic laser papillotomy”) may be an option to relieve discomfort. The procedure involves fragmenting and extracting all visible stones in the kidney with the intent to “unplug” and clear obstructed ducts that may have stones trapped in them. In a paper from three institutions, Gdor and colleagues reported on their experience with a total of 65 patients who collectively underwent 176 procedures. All patients in the study had chronic flank pain and multiple non-obstructing kidney stones. 50 patients had followup information available. The majority of patients who underwent this procedure experienced a reduction in their pain (83%). On average, the duration of pain relief from surgery was 26 months. Of note, 17 of the patients in the study had a diagnosis of MSK and their pain relief was similar to that seen in non-MSK patients.
Posted on: Mon, 29 Dec 2014 20:43:58 +0000
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